The invention relates to a method for determining the mechanical axis of a femur, with which the femur is moved about the hip joint, the movement of the femur is followed via a navigation system by means of a marking element on the femur, position data of the femur obtained therefrom are stored and the position of the mechanical axis of the femur is calculated relative to the same from the various position data of the femur in various positions.
WO 98/40037 describes such a method, wherein marking elements are attached to the hip and to the femur for determining the mechanical axis of the femur, the movement of these marking elements during pivoting of the femur about the hip joint being recorded; the position of the hip joint is determined from the position data of the marking element on the hip, on the one hand, and on the femur, on the other hand, and the mechanical axis of the femur may then be determined from the position of the hip joint and the position of the knee joint determined in a different way.
This method operates reliably but has the disadvantage that an additional marking element must be arranged on the hip bone and this is complicated and, in certain circumstances, entails additional pain for the patient.
The object of the invention is to develop a generic method such that a faultless determination of the position of the mechanical axis of the femur is also possible when a marking element is arranged only on the femur.